Atomic Structure - C1

  • Created by: hollygw
  • Created on: 05-09-22 14:06

Fundamental Particles

Proton = mass is 1, charge is +1.

Neutron = mass is 1, charge is 0.

Electron = mass is 1/1840, charge is -1.

Protons and neutrons are nucleons, held in place by strong nuclear force.

Electrons held by electrostatic forces.

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Mass number, atomic number and isotopes

Isotopes have same number of electrons and protons, but different neutrons so different mass number.

React same way, same electron configuration.

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The arrangement of electrons

First shell = 2

Second shell = 8

Third shell = 18

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Mass spectrometer

Finds an accurate relative atomic mass.

Ar=average mass of 1 atom / twelfth mass of 1 carbon-12 atom.

Mr=average mass of 1 molecule/ twelfth mass of 1 carbon-12 atom.


  • Vaccum = apparatus at vaccum, prevent collisions.
  • Ionisation = electrospray (sample dissolved in volatile solvent, forced through hypodermic needle at high voltage, produces + charged droplets, which get smaller until they are just a single + charged ion). OR electron impact (sample vaporised, high energy electrons fired at it from electron gun, knocks off one electron from each particle).
  • Acceleration = + ions attracted to negative plates, lighter travel faster.
  • Ion drift = ions pass through hole in plate, form beam, travel along flight tube.
  • Detection = lighter ones arrive first, flight times recorded, pick up electron to create current.
  • Data analysis = signal created passes to computer, generates mass spectrum.
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More about electron arrangements

Different shells have different amount of energy.

Order of energy = 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p = order they're written.

Electrons in same orbital must have opposite spins.

See the source image

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Electron arrangement and ionisation energy

Ionisation energy = energy required to remove one electron from an atom.

2nd ionisation energy higher, as it is removing an electron from a positively charged ion.


  • Increase across periods, as nuclear charge increases, so harder to remove.
  • Trend can change, magnesium to aluminium is a decrease, as outler electron of aluminium is in 3p orbital, which is higher energy than 3s, so less energy needed to remove.
  • Trend changes, phosphorus to sulfur, phosphorus has one electron in each 3p orbital, but sulfur has two in one, so there is mutual repulsion, meaning the electron can be removed more easily.
  • Decreases down group, as outer electron is further from nucleus. 
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